ENC support for C#7.0: out var, ref, tuple and pattern matching

[ivanbasov]

Customer scenario

Provides ENC support for C#7.0:

• out var
• ref
• pattern matching
• tuples

Unit tests provided. Also I verified EnC scenarios manually.

Bugs this fixes:

Fixes #17896
Fixes #12436
Fixes #16960
Some works towards #12435

Workarounds, if any

Risk

Low

Performance impact

Low

Is this a regression from a previous update?

Root cause analysis:

How did we miss it? What tests are we adding to guard against it in the future?

How was the bug found?

Planned

[tmat]

[tmat]

This one is not fixed yet: #12435 -- we don't have switch statement working yet.

[jinujoseph]

Do we want to maintain missing switch statement support in pattern matching separately ?

[jcouv]

This change looks good as far as it goes, but I am missing some context. I thought that to enable EnC for C# 7 features (such as switch, out var, deconstruction) we needed at least two things:

• a reasonable distance function for such syntax
• some logic for managing slots (creating new ones, matching and re-using existing ones)

I this rough understanding correct? Have the latter been done already?

[tmat]

@jcouv Yes, that's correct. Ivan did both. The latter didn't need any changes in the compiler as it turned out the right syntax nodes were already associated with the local symbols.

[jcouv]

Very cool. Nice!

[jcouv]

LGTM

[ivanbasov]

Thank you, everybody, for the review and help! I have updated reference to #12435 in the description.

[ivanbasov]

Tagging @MattGertz for Ask mode approval